The present invention relates to an electromagnetic flow coupler which serves to drive liquid and more particularly to an arrangement of an insulator which is suitable to enhance the efficiency of an electromagnetic flow coupler.
The previously known electromagnetic flow coupler is a square flow path type electromagnetic flow coupler as disclosed in Japanese patent unexamined publication JP-A-59-10163. This square flow path type electromagnetic flow coupler prevents current from leaking into the side wall 9 of the flow path by arranging an insulating material 4 on the side wall as shown in FIG. 2. However, since the current which contributes to drive the fluid must flow through a conductive duct 9 as indicated by arrows 11 in FIG. 2, Joule loss (heat) will be disadvantageously produced. To eliminate the Joule loss in the duct, a circular flow path type electromagnetic flow coupler (hereinafter referred to as a circular electromagnetic flow coupler) as shown in FIG. 3 has been proposed. This circular electromagnetic flow coupler permits current to flow in a loop manner in the circumferential direction in the fluid so that the side of the flow path is not insulated. However, actually, due to the difference in electrical conductivity between fluid, e.g. liquid metal sodium and the side wall of an inner tube 1 or outer tube 2, as indicated by arrows 11 in FIG. 3, a part of the current generated in the generator side flow path 5 leaks to the side wall 1 or 2 on the generator side and a part of the current in the pump side flow path 6 also leaks to the side walls on the pump side. Since the current leaks to the side wall in this way, the current produced in the fluid on the generator side is not smoothly propagated to the fluid on the pump side. Thus, force for driving the fluid on the pump side becomes small. Accordingly, the efficiency of the above circular electromagnetic flow coupler will be deteriorated.
In short, the above prior art circular electromagnetic flow coupler provides the following problem to be solved. Since the side wall is not insulated, current leaks to the side wall. Thus, this circular electromagnetic flow coupler can not attain its object, i.e. to eliminate the Joule loss in the side wall. This reduces the current which is to contribute to drive the pump side current, thereby attenuating the efficiency of the circular electromagnetic flow coupler. Further, even if the flow path side is coated with an insulator to prevent the current from leaking to the side wall, a high pressure is exerted to the insulator due to the difference in thermal expansion coefficient between the tube material or the used fluid, e.g. sodium and the insulator, so that the insulator may be damaged or destroyed.